Harry, a native of Madison County, was a veteran of World War II, serving in the Army; enlisted on 22 Mar 1945: discharged 15 May 1946.
Harry retired from GTE and was a charter member of the Memorial Church of Christ.
Harry died of natural causes at age 67, on 21 Feb 1990 in Huntsville, Madison, Alabama and was placed to rest at the Maple Hill Cemetery in Huntsville, Madison, Alabama. Survivors included his wife, Mary Katherine Hall Ford Darnell; two sons, D Darnell of Hazel Green and G Darnell of Birmingham; and two grandchildren. 
Expanded bio with additional sources. I was not able to find substantiation of his retirement or church membership as already existing in the profile.
Added red brackets to referenced family, who most likely need profiles and linking to this bio. I am not related, so feel free to handle if you have an interest.
Wife has brackets and is deceased (i.e.DEATH 28 DEC 2019 • Huntsville, Madison, Alabama, USA ), but is still considered living by her profile manager and therefor can not be linked.
↑ 1.01.1 U.S., Social Security Death Index, 1935-2014
↑ 2.02.12.2 U.S., Department of Veterans Affairs BIRLS Death File, 1850-2010
↑ 3.03.1 U.S., Social Security Applications and Claims Index, 1936-2007
↑ "United States Census, 1930," database with images, FamilySearch (https://www.familysearch.org/ark:/61903/1:1:3JCW-ZMM : accessed 29 November 2020), Harry A Darnell in household of Willian E Darnell, Huntsville, Madison, Indiana, United States; citing enumeration district (ED) ED 9, sheet 14A, line 29, family 318, NARA microfilm publication T626 (Washington D.C.: National Archives and Records Administration, 2002), roll 37; FHL microfilm 2,339,772.
↑ "United States Census, 1940," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:V1PH-8JC : 27 July 2019), Harry Darnell in household of William Darnell, Election Precinct 11, Madison, Alabama, United States; citing enumeration district (ED) 45-35, sheet 2A, line 39, family 23, Sixteenth Census of the United States, 1940, NARA digital publication T627. Records of the Bureau of the Census, 1790 - 2007, RG 29. Washington, D.C.: National Archives and Records Administration, 2012, roll 57.
↑ "Alabama County Marriages, 1809-1950," database with images, FamilySearch (https://www.familysearch.org/ark:/61903/1:1:VZKQ-7R1 : 15 November 2020), Harry Alexander Darnell and Mary Katherine Hall, 06 May 1944; citing Madison, Alabama, United States, County Probate Courts, Alabama; FHL microfilm 1,993,773.